Hydraulic cylinder, especially a trim and tip cylinder for outboard type boat propeller drive units

ABSTRACT

A hydraulic cylinder provided in its piston with axial channels with check valves permitting fluid flow in one direction from one cylinder chamber to the other. Constricting means in the form of a spring-biased plate displaceably mounted on the piston rod covers, after a certain displacement of the piston, a portion of the outlet openings of the axial channels to reduce the flow-through cross-sectional area and brake the piston movement.

The present invention relates to a hydraulic piston-cylinder device,especially intended for trimming or tipping an outboard type boatpropeller drive, comprising a cylinder, a piston displaceable in thecylinder, dividing the interior of the cylinder into two cylinderchambers, and a piston rod joined to the piston and extending outthrough an opening in one cylinder end wall, said piston having at leastone axial through-passage with stop valve means permitting fluid to flowin one direction through the piston from one cylinder chamber to theother.

In, for example, one known boat propeller drive, a pair of trim and tipcylinders of the type described above are arranged between the driveshield and and rig, each cylinder being articulated in the shield andengaging the rig with the associated piston rod. When trimming out ortipping up the rig, hydraulic fluid is supplied to the cylinder chamberon the piston side, whereupon the cylinder chamber on the piston rodside is drained to a tank. If the rig during operation strikes an objectin the water, which forces the rig to be tipped up, hydraulic fluid canflow through the passage in the piston from the cylinder chamber on thepiston rod side to the opposite cylinder chamber if the force on the rigis so great that the fluid pressure created on the piston rod sideexceeds the pressure on the opposite side, which permits rapid extensionof the piston rod and rapid tipping of the rig. In this manner, the riskof serious damage to the rig is reduced when running aground, forexample. In a known design of a boat propeller drive of the typedescribed, a rubber buffer is used between the shield and the rig as anend abutment so that rapid tipping of the rig will not cause damage tothe drive.

The purpose of the present invention is to achieve a piston-cylinderdevice of the type described by way of introduction which isparticularly, but not exclusively, intended to be used in a tippableboat propeller drive by making it possible to vary the resistance topiston movement caused by an external force, depending on the positionof the piston in the cylinder.

This is achieved according to the invention by virtue of the fact thatconstricting means cooperating with the piston are arranged, after acertain piston movement in the direction resulting in fluid flow fromone cylinder chamber to the other via the check valve means to reducethe flow-through the area of the axial passage to brake continued pistonmovement.

A piston-cylinder device of this type can, for example, be used as atrim and tip cylinder in a boat propeller drive so that if the rigcollides with a floating object or runs aground, it will provide lessresistance to piston movement during initial tipping up of the rig and,after a certain piston movement, representing a certain tipping upangle, will increase this resistance and provide controlled breaking ofthe swing movement, so that, inter alia, the need for a rubber buffer iseliminated.

The invention will be described in more detail with reference toexamples shown in the accompanying drawings, where

FIG. 1 shows a schematic side view of a boat propeller drive of outboardtype,

FIG. 2 shows a partially sectioned side-view of certain components inthe rig suspension of the drive, and

FIG. 3 is a longitudinal section through one embodiment of apiston-cylinder device according to the invention.

FIG. 1 shows a propeller drive which is known per se of so-calledAquamatic® type, comprising a shield 1 designed to be solidly mounted inan opening in a boat transom. A propeller rig, generally designated 2,is suspended in a forked supporting bracket 3, which is pivotallymounted in the shield 1 for pivotal movement about a horizontal pivotaxis 4. A pair of hydraulic piston-cylinder devices 5 (one shown in FIG.2) are arranged symmetrically relative to a centre plane of thepropeller drive. Each cylinder is pivotally mounted in the shield 1,while the associated piston rod 7 is mounted in the supporting element3. The cylinder 6 is coupled into a hydraulic circuit (not shown in moredetail here) via lines 8 and 9. When hydraulic fluid is supplied to thecylinder chamber 10 (see FIG. 3) via line 8, fluid is drained from thecylinder chamber 11 via line 9, and the rig 2 is trimmed out, i.e. itsangle relative to the shield 1 increases.

A piston 12 joined to the piston rod 7 has, as is indicated in FIG. 3, anumber of axial through-channels 13 evenly distributed about a circle,each of which containing a check valve element 14 in the form of aspring-biased ball, which under all operating conditions, blocks liquidflow in the direction from cylinder chamber 10 on the piston side tocylinder chamber 11 on the piston rod side, but permits fluid flow inthe opposite direction, if the pressure in cylinder chamber 11 shouldexceed the pressure in cylinder chamber 10. This can, for example, occurif the rig 2 strikes an object in the water or runs aground, so that theoutwardly directed force on the piston rod 7 and the piston 12 willcreate a sufficiently great increase in pressure in cylinder chamber 11.The fluid can then be rapidly evacuated from the cylinder chamber 11into cylinder chamber 10 to permit a rapid tipping up of the rig, thusreducing the risk of serious damage to the rig.

In known propeller drives of the type described, the rig can in generalbe tipped up so that its lower end lies somewhat above the surface ofthe water, with the aid of the described cylinder device 5. This meansthat the upper end of the rig in certain cases can strike the shield andto reduce the risk of damage in such a case, a rubber buffer is usuallymounted on the shield to absorb the impact.

There is, however, no need for continued rapid tipping movement of therig when it has left the water. Instead, it is desirable to brake themovement. According to the invention, a constricting element in the formof a circular plate 20 is arranged in the cylinder 6 to provide thisbraking function. The plate 20 has a central bore 21 for displaceablemounting on the same on the piston rod 7. The outer diameter of theplate 20 is adapted to the inner diameter of the cylinder, so that theplate can easily slide in the cylinder. The plate is provided on itsside facing the piston 12 with a shoulder 22, the radius of which isapproximately equal to the radius "r" of the circle on which the centresof the axial channels 13 lie. This means that the shoulder 22 will coverapproximately half of the outlet of the channels 13 and thus reduce theflow-through area by approximately one half, when the plate lies in theposition shown with solid lines in FIG. 3. A helical spring 24 placedbetween the end wall 23 of the cylinder 6 and the plate 20 keeps theplate 20 in its unloaded state in this position.

Normally, during operation, the piston 12 is at or near the positionshown with dash-dot lines in FIG. 3. If the piston rod 7, for one of theabove-mentioned reasons, is subjected to a sudden outwardly directedforce, the piston 12 will first move rapidly from the position shownwith dash-dot lines to the position shown with solid lines, thanks tothe relatively great total flow-through area of the axial channels 13.When the plate 20 comes into contact with the piston 12, theflow-through area is reduced to approximately half of the original,which results in a constriction of the flow through the piston and abraking of the piston movement during the remaining portion of the pathof movement of the piston.

Even though the piston-cylinder device according to the invention hasbeen described with reference to a preferred application, it is ofcourse also possible to use it in other contexts, where one can utilizethe described functional principle of variable resistance.

We claim:
 1. In a hydraulic piston-cylinder device, comprising acylinder, a piston which is displaceable in the cylinder and whichdivides the interior of the cylinder into two cylinder chambers, and apiston rod joined to the piston and extending out through an opening inone cylinder end wall, said piston having at least one axialthrough-passage with check valve means permitting fluid flow in only onedirection through the piston from one cylinder chamber to the other andpreventing fluid flow from said other cylinder chamber to said onecylinder chamber; the improvement comprising means (8, 9) for connectingthe cylinder in a hydraulic circuit to drain fluid from said onecylinder chamber (10) and to supply fluid to said other cylinder chamber(10), and constricting means (20) cooperating with the piston (12) andarranged, after a certain piston movement in the direction resulting influid flow from said one cylinder chamber (11) to said other (10) viathe check valve means (14), to reduce the flow-through area of the axialpassage (13) to brake continued piston movement.
 2. Device according toclaim 1, characterized in that the check valve means (13) are arrangedto permit fluid flow from the cylinder chamber (11) on the piston rodside to the opposite cylinder chamber (10) and that the constrictingmeans comprise a valve element (20) moveably mounted in the formercylinder chamber, said element after a certain piston movement uponcontact with the surface of the piston (12) facing the piston rod (7),covers a portion of the outlet opening of said passage (13).
 3. Deviceaccording to claim 2, characterized in that between the valve element(20) and the inside of said cylinder end wall (23), inset spring means(24) press the valve element against the piston surface after a certainpiston movement.
 4. Device according to claim 2, characterized in thatthe valve element is a circular plate (20) displaceable on the pistonrod (7) and having a circular shoulder (21) facing the piston (12), saidshoulder, upon contact with the piston, covering a portion of the outletopening.
 5. Device according to claim 4, characterized in that thepiston (12) has a plurality of axial passages (13) evenly distributedalong a circle and provided with check valve means (14), said axialpassages having circular cross-section and their centres lying on aradius approximately equal to the radius (r) of the outer edge of theshoulder (21) of the plate (20).
 6. In a boat propeller drive,comprising a shield intended to be solidly joined to the transom of aboat, a propeller rig, which is suspended in the shield for pivotalmovement relative thereto about a horizontal pivot axis, and at leastone hydraulic piston-cylinder device operating between the shield andthe rig, the cylinder of said device being pivotably joined to eitherthe shield or the rig, the piston rod joined to the piston extendingthrough an opening in one cylinder end wall and engaging the other oneof said components, said piston dividing the interior of the cylinderinto two cylinder chambers, and having at least one axialthrough-passage with check valve means permitting fluid flow in only onedirection through the piston from the cylinder chamber on the piston rodside to the other cylinder chamber; the improvement comprising means (8,9) for connecting the cylinder in a hydraulic circuit to drain hydraulicfluid from the cylinder chamber (11) on the piston rod side and tosupply fluid to said other cylinder chamber (10), and constricting means(20) cooperating with the piston (12) and arranged, after a certainpiston movement in the direction towards the piston rod side, to reducethe flow-through area of the axial passage (13) to brake continuedpiston movement.
 7. Boat propeller drive according to claim 6,characterized in that constricting means are formed by a circular plate(20) displaceably mounted on the piston rod (7) and having a circularshoulder (21) facing the piston (12), said shoulder, upon contact withthe piston, covering a portion of the outlet opening of said passage(13), and that between the plate and the inside of said cylinder endwall (23) inset spring means (24) press the plate against the pistonsurface after a certain piston movement.
 8. Boat propeller driveaccording to claim 7, characterized in that the piston (12) has aplurality of passages (13) distributed evenly along a circle andprovided with check valves (14), said passages having circularcross-section, the centres of which lying on a radius (r) approximatelyequal to the radius of the outer edge of the shoulder (21) of the plate.